The present invention relates to a method and an apparatus for depositing a thin film and a multilayer film using a photo-induced CVD (chemical vapor deposition) technique which is widely used in the industry.
The photo-induced CVD technique has been used to deposit various thin films or multilayer films. The photo-induced CVD technique has a problem in that a film is deposited on a window through which light is introduced into a reaction chamber during film deposition. The film deposited on the window decreases the intensity of the light irradiating the material gas in the reaction chamber through the window, thereby decreasing the film deposition rate at which the film is deposited onto a substrate. A conventional approach to solve this problem is blowing inert gasses such as argon, helium, etc. onto the window as disclosed, for example, in Japanese patent laid-open No. 183921/'86 or 169384/'88. Also, known is a method of etching the film deposited on the window by irradiating light of different wavelength disclosed in, for example, Japanese patent laid-open No. 263213/'86.
An example of the conventional technique to prevent the light introducing window from becoming clouded by blowing inert gas is described hereunder by reference to FIG. 7.
FIG. 7 is a configuration diagram of a conventional thin film depositing apparatus using a photo-induced CVD technique. In FIG. 7, represented by reference numerals 71, 72, 73, 74, 75, 76, 77 and 78 are a reaction chamber, a substrate holder, a substrate, an evacuation orifice, a reactive gas intake, light from a light source, a light introducing window, and a purging gas intake, respectively.
A film depositing process of the thin film depositing apparatus as constructed above will be described hereunder. Firstly, the substrate 73 on which a film is deposited is placed on the substrate holder 72 in the reaction chamber 71. The reaction chamber 71 is closed and evacuated through the evacuation orifice 74 to achieve high vacuum in the reaction chamber 71. The substrate 73 is then heated to a predetermined temperature before introducing a reactive gas into the reaction chamber 71 through the reactive gas intake 75. Subsequently, light 76 is irradiated through the light introducing window 77 to decompose the gas for deposition of a film on the substrate 73. Simultaneously, an inert gas is introduced through the purging gas intake 78 to prevent the reactive products from depositing on the light introducing window 77.
However, a disadvantage of the conventional system is incomplete prevention of clouding of the light introducing window due to the long time duration required for film deposition. This results in inaccurate film thickness and frequent replacement of the light introducing window. The problem is further exacerbated in applications using a large light introducing window for large-area film depositions and in applications using irradiation light with higher intensity.
On the other hand, if light intensity is not uniform over the light introducing window, the thin film deposited on the window varies in thickness, i.e., it is thicker at the area where light intensity is higher. This acts to correct the irregularity in light intensity to be introduced in the reaction chamber. However, the conventional apparatus is not controlled to utilize this type of effect.
The present invention intends to solve the above problems of the conventional apparatus. It is, therefore, an object of the present invention to provide a method and an apparatus for depositing a thin film and a multilayer film which compensates for the decrease in film deposition rate due to clouding of the light introducing window. It is another object of the present invention to provide a method and an apparatus for depositing a thin film in a manner overcoming non-uniformities in light intensity.